1. Field of the Invention
The present invention pertains to an electronic system (such as, without limitation, a multilevel power inverter or an active front end) that employs multiple modules (wherein each module may include one or more printed circuit boards (PCBs) and/or other electronic components), and, in particular, to a communications architecture for providing data communication, synchronization and fault detection between isolated modules in such an electronic system.
2. Description of the Related Art
A number of different power conversion modules/systems are well known for converting power from one form to another. For example, a multilevel power inverter is a power electronic device that is structured to produce AC waveforms from a DC input voltage. As another example, an active front end (also called a controllable rectifier) is a power electronic device wherein AC waveforms are converted to DC voltages. Such power conversion modules/system are used in a wide variety of applications, such as, without limitation, variable speed motor drives, and frequently require highly synchronized timing across communication links of the system and/or fast fault response between links in the system.
Many current industrial electronic systems employ asynchronous data communications (wherein no serial clock (SCLK) is employed) and require specialized physical interfaces and topologies. These asynchronous topologies require one of the following solutions to provide synchronization: (i) timestamp messages, which require dedicated hardware and processing time, or (ii) a completely separate communication line used solely for synchronization (which adds additional connections such as additional optical fibers).
Many current systems utilize the timestamp method to keep synchronization. A case example is the IEEE 1588 specification which allows synchronization across Ethernet networks. The standard requires that specialized timestamp hardware be included in each node's Ethernet system. Additionally, a central hub/switch must also be added to the system to meet the standard Ethernet star topology. While only two optical fibers would be needed for each module to implement such a system, the central hub/switch would also need two optical fibers. Unfortunately, fiber optic Ethernet hubs/switches are not as common or cost effective as their copper counterparts. Additional downsides include sacrificing some of the communication bandwidth to provide time for the synchronization messages to be broadcast.
In addition, the well known EtherCAT® system is a variant of the IEEE 1588 specification where the synchronization is done entirely in hardware, and a ring topology is used instead of a star. No switches are required, but each module must have two datapaths to provide round trip information, which is needed for the synchronization. These two data paths require four fiber transceivers per module (2 Rx/Tx pairs). Also, the required EtherCAT® hardware interface integrated circuit (IC) adds additional cost and integration effort.
None of the standard communication solutions appears to provide a dedicated way to flag a fault quickly without sending a specific data message (note that sending a fault data message is not desirable as the message must be fully received and decoded before fault actions can occur, leading to relatively slow detection performance). The common way to provide a fast fault line has been to provide a dedicated healthy line that any node on the system can pull down when a problem is detected. The problem with such a system is that it requires an additional fiber interface that is not part of the actual communication scheme.
Thus, there is a need for a communication architecture that provides an efficient way to communicate data and synchronization information that may be employed in an electronic system such as, without limitation, a power conversion module/system (e.g., a multilevel power inverter or an active front end).